In a wireless communications network, each device needs to transmit information by using a frequency resource. The frequency resource is also referred to as a spectrum. Spectra may be classified into a licensed spectrum and an unlicensed spectrum. The licensed spectrum is a dedicated frequency resource of some operators, and the unlicensed spectrum is a shared frequency resource in the wireless communications network. With development of communications technologies, there is an ever-increasing amount of information transmitted in the wireless communications network. Preemption of the unlicensed spectrum for information transmission may increase a data throughput in the wireless communications network to better meet a requirement of a user.
However, in the prior art, after a device successfully preempts a channel of the unlicensed spectrum, because a data sending moment may be random, a moment for sending data by the device may not be a starting moment of a complete subframe. In this way, a receiving device needs to continuously perform blind detection on the channel to determine a moment at which data transmission is started. As a result, the receiving device has excessively large power consumption.